The present invention is in the field of electronic mail and, more particularly, is directed to verification, by a receiver of an e-mail message, of the integrity of the received e-mail message.
Electronic mail has become a useful tool in our personal and business lives. Unfortunately, like other useful technologies, it has also become an intrusion. For example, only the most diligent among us are able to avoid scurrilous attempts to sell us nutritional supplements, mortgages, pornography and numerous other “products.” More recently, scammers have taken to using “spoof” e-mails in an illegitimate attempt to gain access to our personal information. For example, such scammers have spoofed BestBuy and eBay, attempting to entice unsuspecting users into providing personal information such as social security numbers and credit card numbers. Thus, as useful as e-mail has proven to be in our lives, it can be dangerous to blindly assume that received e-mail is legitimate. However, efforts at minimizing intrusion of technologies often unavoidably diminish the usefulness of the technology whose intrusion we are seeking to minimize.
For example, “spam” catchers typically catch legitimate e-mail messages in addition to spam e-mail messages. Users must carefully scrutinize the caught e-mail messages, lest any of them be legitimate and unintentionally ignored. Also, spoof e-mail messages are more difficult to detect, as they appear in many respects to be legitimate.
There have been a number of attempts to address the concerns with e-mail. One notorious attempt is described in U.S. Pat. No. 5,999,967, to Sundsted. Sundsted has proposed attaching an “electronic stamp” to each e-mail message sent, where the receiver of the e-mail message receives money from the sender. The receiver can determine whether it is “worth it” (from the value of the attached stamp) to read the e-mail and receive the money. Because Sundsted employs “stamps” having monetary value associated with them, there is a practical requirement (which is difficult to achieve) that the system to exchange value be secured against fraud. Furthermore, even if the system to exchange value can be made secure, there is nothing that allows a receiver of e-mail to discriminate between senders from whom it is desirable to receive e-mail and senders from who it is undesirable to receive e-mail apart from the monetary benefit to the receiver who reads e-mail. Perhaps even more significantly, nothing in the electronic stamp allows one to assess the integrity of the e-mail.
In many respects, a proposed system known as “HashCash” is similar to the system described in the Sundsted disclosure. The proposed HashCash system is such that, before an e-mail message is sent, a significant particular math computation must be performed on the sending computer to generate a token. This computation is such that, for example, it would take up to 15 seconds on a standard 1 GHz PC. The token is incorporated into the e-mail message. The receiving computer performs a relatively simple computation to verify that the token is, in fact, the result of the particular a math computation performed on the sending computer. A drawback of HashCash, then, is that anyone who is willing to undergo the computational burden can send e-mail messages unimpeded. That is, like the system described in the Sundsted patent, there is nothing in the token that allows the receiving side to discriminate between senders from whom it is desirable to receive e-mail and senders from whom it is undesirable to receive e-mail, beyond verifying that the sender did, in fact, incur the computational expense to generate the HashCash token. That is, in some sense, HashCash merely substitutes computational expense for the monetary expense of the Sundsted system (albeit there is money or other value received by the e-mail recipient).